SUMMARY/ABSTRACT Congenital anomalies of the lymphatic vasculature arise due to defects in lymphatic development and are increasingly detected in utero. The lymphatic vasculature is responsible for maintaining tissue fluid homeostasis, interstitial hormone levels, immune surveillance, and intestinal lipid absorption. Disruption of these functions by anomalous lymphatics can impose significant morbidities on affected individuals, including hemorrhage, bony deformities, respiratory compromise, intestinal dysfunction, and sepsis. Lymphatic anomalies are relatively common among congenital conditions (individual occurrence from 1:3500 to 1:10,000 births) and contribute significantly to the population requiring intensive care, beginning in the prenatal period. These patients go on to accumulate severe lifelong consequences of these conditions. Despite this, the genetics of lymphatic anomalies are poorly understood and there is a paucity of relevant mouse models, limiting prenatal diagnosis and the development of effective treatments. Different subtypes of lymphatic anomalies have been shown to arise from germline and somatic mutations. However, the genetic causes of the vast majority of lymphatic anomalies remain unknown. To further understand lymphatic anomaly genetics and pathobiology, we propose to develop a bedside-to-bench approach to identify and characterize genetic mutations. We hypothesize that affected-lymphatic endothelial cells isolated from fetal anomaly specimens, as well as parental-fetal germline specimens, can be used to comprehensively screen for novel lymphatic anomaly mutations. We propose to bring together and establish a multidisciplinary clinical and basic research team with expertise in prenatal and pediatric lymphatic anomalies, and human genetics. In Aim 1, we propose to develop a fetal lymphatic anomalies program to isolate affected lymphatic endothelial cells from fetal lymphatic anomalies and subject them and fetal-maternal-paternal trios to WES and cohort analysis. Our initial analysis of a small set of lymphatic anomalies fetal-maternal-paternal trio data identified a loss-of-function mutation in Rere as a likely pathological mutation in a fetal cystic hygroma. Rere is a positive regulator of retinoic acid signaling, a pathway known to function in lymphatic development. In Aim 2, we propose to develop a novel mouse model in which we delete lymphatic endothelial Rere and determine its role in lymphatic development. The goal of this pilot grant is to develop a precision medicine program at Columbia University that is effective at identifying and characterizing the genetic causes of lymphatic anomalies. Findings will be used to generate preliminary data for mutli-PI R01s and Program Project Grants to be submitted by the multidisciplinary team. These studies also aim to identify and understand how novel genes and pathways function in lymphatic development and homeostasis.